Vilanova, who replaced Pep Guardiola this summer, underwent surgery on a salivary gland last November. Media reports in Spain suggest the 44-year-old Vilanova has suffered a relapse.
Barca released a press statement on Wednesday morning announcing they had suspended all activities for the day but did not go into details and did not mention Vilanova.
The statement read: "Barcelona announce that it is has suspended the press conference from president Sandro Rosell planned for midday. As well as that, the media Christmas lunch has been cancelled.
"Later today the club will issue a further release. Until that time we will not make any announcement about this matter. We regret any inconvenience this decision may cause."
- Pep Guardiola